The present invention is the preferred method for manufacturing the padded or cushioned strap disclosed in our related application Ser. No. 538,538, filed Jan. 6, 1975, now U.S. Pat. No. 3,952,383 entitled "Strap Fitting for Automobile Interior and Other Uses" and our related application Ser. No. 653,668, now U.S. Pat. No. 3,977,054, filed (same day as this application), entitled "Strap Fitting For Automobile Interior and Other Uses", which is a continuation-in-part of the first mentioned related application. The teachings of said related applications are incorporated in this application by reference thereto.
The strap disclosed in the above referenced applications has met with great commercial success in the automotive industry. As a result, a wide variety of applications for such straps had developed, such as door pulls, as passenger entry/exit assist straps and as seat back assist straps. These applications generally require multiple strap installations in each vehicle, and, in that this strap has been adopted for use in numerous different makes and models of vehicles, it becomes readily apparent that the method and apparatus for manufacturing these straps must be both reliable and capable of extremely high volume production in order to meet the demands of the automobile industry. Further, as in any high volume production article, the method must be economical and efficient to perform.
Also, in that the success with which the strap has been greeted is due at least in part to the fact that the strap offers a smooth, wrinkle-free surface having a cushioned soft feeling of elegance, the methods and apparatus for manufacturing them must be capable of achieving these objectives as well as being suitable for use with a wide variety of outer coverings and trim strips so as to allow production of straps which will blend with or accentuate a wide variety of decors. In order to achieve these results, it is important that the apparatus accurately position the strap components relative to each other, slightly compress the cushioning material as the outer wrap is applied, and that the covering material be tensioned slightly both laterally and longitudinally. It is readily apparent that to manufacture this strap even by hand would be a difficult, tedious and time consuming operation; and to adapt machinery and methods capable of high production capacity with a minimum of time and expense while still producing straps identical in appearance, serves to multiply and compound the problems associated therewith.
The present invention provides a solution to these problems through a method and apparatus which is capable of high volume production, is economical both in labor and materials, and produces a strap having the luxurious soft cushioned feel, as well as an elegant, distinctive, smooth, wrinkle-free appearance.
In the method and apparatus of the present invention, the vinyl wrap or cover is longitudinally tensioned by securing the ends of the vinyl wrap on a base member of a fixture. This can be conveniently accomplished by providing small holes through the vinyl wrap near its ends and by providing pins which protrude from the base member of the fixture to receive the holes in the vinyl wrap while the wrap is longitudinally tensioned. The wrap remains longitudinally tensioned in this manner throughout the assembly process on the fixture as described hereinafter. The foam member is centrally positioned on the tensioned vinyl wrap and the structural strap member is centrally positioned on the foam member. In the preferred construction of the padded strap, the main structural member is provided with an adapter strip having an uncercut groove which receives the adapter strip. Additionally, the main structural member has a plastic adhesive coating on its surface opposite the foam member.
With the vinyl wrap, foam member and main structural strap in position, the foam member is compressed by applying a force across the main strap member and the vinyl wrap. Conveniently, this is accomplished by bearing a clamping bar on top of the main strap member with a predetermined force which compresses the foam member. The clamping bar also serves to secure the vinyl wrap, the foam member and the main structural strap member in their symmetrical positions. The fixture is provided with a pair of hinged jaws, one hinged to each side of the fixture base member. The hinged jaws rotate upwardly and inwardly while bearing against the vinyl wrap so as to transversely tension the vinyl wrap and to wrap the vinyl wrap about the foam member and the structural strap member. Rotation of the jaws continues until the jaws are positioned above the upper surface of the main strap member.
When the clamping bar is removed, the foam expands to bear the upper portion of the wrapped strap assembly against the hinged jaws. This bearing force is sufficient to maintain the precompression of the foam member, to maintain the transverse tensioning of the vinyl wrap, and to maintain the vinyl wrap, the foam member and the structural strap member in position after the clamping bar is removed. At this point in the method, the longitudinal ends of the vinyl wrap lie on the upper surface of the strap member and are transversely opposed. A trim strip is then positioned across the opposed longitudinal edges of the vinyl wrap. After positioning of the trim strip, a dielectric sealing bar is forcibly engaged with the vinyl trim strip and the trim strip is joined to the vinyl wrap by passing high frequency energy between the dielectric sealing bar and the structural strap member. Preferably, the dielectric joining process joins the trim strip, the opposed longitudinal edge portions of the vinyl wrap, and the plastic coating material on the main strap member so that the trim strip, the vinyl wrap and the main strap member are each secured to the other.
At this point in the method, the assembly is removed from the fixture for further processing. The strap is bent to provide it with a configuration which is suited for its intended use. Thereafter, the padded strap assembly is placed in an oven for heating at a predetermined temperature for a predetermined period. The temperature and period of heating is selected so as to shrink the vinyl wrap sufficiently to remove wrinkles which may have formed during the bending operations.
In view of the above description of the preferred method of this invention, it will be appreciated that a convenient apparatus and procedure is provided for tensioning the vinyl wrap both longitudinally and transversely, to prestress the foam member during wrapping of the strap, to maintain the prestress of both the foam member and vinyl wrap during the dielectric adhesion process, and to ultimately provide a strap construction having the appropriate compression of the foam member, tensioning of the vinyl wrap, and which is substantially wrinkle free.